The present invention relates to a structure of an electromagnetic valve for opening and closing a fluid flow passage in a hydraulic/pneumatic system using oil or air.
In general, a purpose of an operation is achieved by controlling an operation fluid in a hydraulic or pneumatic system. In such a hydraulic/pneumatic system, an electromagnetic valve is used as means for opening and closing a passage of fluid flow.
Such kinds of hydraulic or pneumatic systems have been adopted in automotive vehicles ,for example, in vehicular air (pneumatic) suspension systems.
Since the present invention is particularly applicable to electromagnetic valves in such air suspension systems, a construction of the air suspension system will generally be described below.
Since the air suspension system can achieve a lower suppression of inherent vibrations generated by vehicle body and spring systems as compared with other suspension systems, it can absorb large vibrations transmitted to the vehicle body. In addition, since the air suspension system itself has an attenuation characteristic, it can also absorb fine vibrations generated from load surfaces. Consequently, driving comfortability of the vehicle can be improved.
Furthermore, since the air suspension system can always maintain a height of the vehicle body constant regardless of a load applied to the vehicle, an improvement in appearance of the vehicle (e.g., appropriation of an upright member due to a lowered trailing portion of the vehicle body) and shortening of a stroke of the suspension can be achieved. During driving of the vehicle, the air suspension system can select appropriate spring constant in correspondence to magnitudes of roughness on road surfaces and driving conditions.
In this way, the air suspension system has two control functions:(a) a vehicle height adjustment; and (b) spring constant switching.
A Japanese Utility Model Application first (non-examined) Publication (Jikkai) No. sho 60-85206 published on June 12, 1985 exemplifies the electromagnetic valve used in the air suspension system having the above-described functions.
The disclosed electromagnetic valve is ,e.g., used as a cutoff valve in the air suspension system and controls the opening and closing of a passage intervened between a main chamber provided therein and sub tank installed in the air suspension system.
However, the disclosed electromagnetic valve in the above-identified Japanese Utility Model Application publication has many drawbacks. In detail, since the electromagnetic valve has a main valve only through which the flow passage of the operation fluid (air) is opened or closed, a pressure difference occurs in front and rear portions of the main valve when the main valve is operated to close the passage of the air flow. Therefore, a spring force of a spring and magnetic attracting force of a solenoid become necessary which can resist against a load generated by the pressure difference. Consequently, the spring and solenoid become unnecessarily large-sized. It becomes difficult to make these components small-sized, light-weight, and to make the solenoid economical in power consumption. Furthermore, since the large attracting force is required for the solenoid, a large operating noise from the electromagnetic valve is consequently induced.